With the development of broadband access technology, Data Subscriber Loop (DSL) technology that is used for subscriber loop access is gradually becoming a main and widely applied broadband access technology. Subscriber lines are laid for common narrowband telephone service. However, frequency band and speed of DSL is 10 to 1000 times greater than that of common narrowband telephone service. Furthermore, development of DSL service is affected due to some problems concerning with subscriber lines, such as long-term laying, poor maintenance, large environment interference and long distance. In order to satisfy requirements for opening line pre-selection and breakdown maintenance of DSL service, subscriber line testing technique has gradually being developed.
At the present time, subscriber line testing technique has been highly valued by both device manufactures and telecom service providers, henceforth applied in a large scale.
Generally, a broadband line testing module for implementing subscriber line testing is placed in a Digital Subscriber Line Access Multiplexer (DSLAM) end. The broadband line testing module is connected to the subscriber lines to be tested, evaluating line quality and judging line breakdown by using different broadband testing techniques, thereby implementing single-terminal broadband testing for subscriber lines, as is shown in FIG. 1.
The object of subscriber line testing is to test those subscriber lines loading DSL. However, for the existence of Remote Terminal Unit (RTU) in user end, when breakdown is tested, there is no way to confirm whether the breakdown is from the subscriber line or RTU, thereby affecting precision of the present subscriber line testing technique, even disabling some certain subscriber line testing techniques. Consequently, when testing with the present subscriber line testing technique, the subscriber is often telephoned and required to manually disconnect RTU from the subscriber line; after completion of testing subscriber line procedure, the subscriber is telephoned again to connect RTU up. The RTU includes RTU of Asymmetrical Digital Subscriber Loop (ADSL), Very-high-speed Digital Subscriber Loop (VDSL), or Single-line-pair High-bit-rate Digital Subscriber Loop (SHDSL).